1. Field of the Invention
The present invention relates to an electrodeposition solution for forming a fine pattern to be used for producing an optical part utilizing light rays in an infrared (IR) region, particularly an optical part such as a various types of information processing elements, optical circuit elements and the like, which are formed on a substrate such as an optical waveguide, an optical part produced by using the electrodeposition solution, and a production method for the optical part.
2. Description of the Related Art
As a material to be employed for forming an optical waveguide for an optical circuit, inorganic materials such as quartz, a variety of glass materials, light transmissive oxide type ferroelectrics and the like and a variety of polymer materials have been used. Among these materials, as compared with an inorganic material, a polymer material easily forms a thin film by a spin coating method, a dipping method and the like, is flexible and in addition to these points, polymer material is suitable for producing an optical waveguide with a large surface area.
Further, in a thin film formation method using such a polymer material, as compared with a thin film formation method using an inorganic material such as quartz, a heating step using a high temperature at the time of thin film formation is not required. Therefore, use of a polymer material has an advantage in that an optical waveguide can be formed even on a substrate such as a semiconductor substrate, a plastic substrate and the like, for which are difficult to subject to heating treatments at high temperature. Further, production of a flexible optical waveguide utilizing the flexibility and toughness of a polymer material is made possible.
Accordingly, economical mass production of an optical waveguide part for an optical integrated circuit to be employed in optical communication, an optical wiring board to be employed in a field of optical information processing and the like from a polymer material for optical use has been desired.
Conventionally, such a polymer material for optical use was inferior in environmental resistance and weathering resistance such as heat resistance, moisture resistance and the like, so that there were problems regarding retention of stability of optical characteristics, however, recently, improvements have been made. Further in a case in which a photosensitive polymer material is used as a polymer material for optical use, formation and processing in production are extremely easy and the mass productivity is also excellent.
However, a photosensitive polymer material employed conventionally is a polymer material in a solid state at a room temperature and when a thick film is formed using the photosensitive polymer material, scattering in a UV region and a visible light region becomes significant and the light transmissivity is deteriorated. Further, in the case of forming a pattern just like an optical waveguide by a photolithographic method or the like, the resolution deteriorates at the time of curing the photosensitive polymer material. Therefore, even if a conventional photosensitive polymer material is used to produce an optical waveguide or the like, a pattern can not be produced as designed with a sufficiently high regeneration and it results in an undesirable effect of a transmission loss of the produced optical waveguide or the like.
Further, since in such a conventionally used photosensitive polymer material as described above consideration regarding properties necessary for an optical material such as decrease of the transmission loss in wavelength region to be used for information transmission is insufficiently, it also has a defective point that the optical waveguide loss is high. Therefore, an optical part of an optical waveguide or the like produced from such a photosensitive polymer material is unsatisfactory in terms of practical use and durability.
As a means for solving the above-mentioned problems, a method for forming a pattern of an optical waveguide or the like using a photocurable resin in a liquid state at room temperature instead of the polymer material in a solid state at room temperature has been considered. However, since the photocurable resin has fluidity, the coating film thickness would change after application of the photocurable resin and a pattern of an optical waveguide or the like could not be formed with good reproducibility and controllability.
Further, in the case of pattern formation using a conventional photosensitive polymer material, etching treatment or the like is needed and thus there are disadvantages in that a large quantity of a harmful alkaline waste solution is generated; the production cost is high due to a large number of processing steps; and that the production line becomes complicated, long and large.
On the other hand, today, as light rays to be used as optical communication means for transmitting a large quantity of information in a long distances, infrared rays in a wavelength range of 1.3 μm to 1.5 μm are generally used in order to suppress attenuation in a quartz material, which is a main material of optical waveguide parts employed for such optical communication. Further, from now on, the needs for transmitting a large quantity of information based on the utilization of light as information transmitting medium are expected to rapidly expand in information transmission and processing not only in a conventional long distance but also in local areas (short distances) such as conventional households and offices.
The optical material used for such transmission and processing of large quantity of information in local areas is required to have suitable properties to be able to be processed and formed into complicated shapes such as connectors and various optical circuits such as an optical waveguide in addition to being mainly used in the form of an optical fiber-like shape for long distance communication and to have various functions such as ease of connection and the like. However, although there is no problem at all in terms of the transmission loss, the quartz material is a fragile material and therefore has inferior processibility and formability, and is difficult to handle and form into a complicated patterns. Accordingly, the quartz material is technically difficult to use as an optical material for local areas.
Thus, a resin material is being paid attention for the processibility, formability and ease of handling of the resin material as an optical material for information transmission in local areas. As compared with the quartz material, the resin material is inferior regarding the transmission loss and the transmissivity in the IR region employed in the optical communication. However, with respect to the transmission loss, since the transmission distance is a short distance, transmission loss as low as that of the quartz material is not required and therefore, it is possible to use even the resin material sufficiently.
Further, since a conventional resin material contains many hydrogen atoms in its molecule, the transmissivity in the IR region of the resin material is insufficient for the optical communication which will be required in the future. However, converting the light rays with a wavelength in a wavelength range of 1.3 to 1.5 μm, which range is utilized for long distance communication, into light rays with wavelength shorter than 850 nm and then distributing the light rays with wavelength shorter than 850 nm to local areas is being researched. If the light rays are such IR rays with wavelength as short as 850 nm, even the resin material is thought to be sufficient for practical application.
For example, according to Maruno, et al. (Maruno, Journal of Electronic Information and Communication Society, Vol. 84, No. 9, pp. 656–662, 2001), it is reported that substitution of hydrogen atoms contained in the resin material with other atoms makes the resin material able to deal with optical communication in the IR region although this is not practical.
Further, as the optical part using the IR transmissive resin material, for example, an optical transmission body obtained by substituting hydrogen atoms contained in an organic polymer, which forms the core part having an initial transmission loss of 0.4 dB or lower at 780 nm wavelength, with heavy hydrogen atoms or fluorine atoms is proposed in Japanese Patent No. 2,854,669. Also, a flat type plastic optical waveguide using heavy hydrogenated or halogenated polyacrylate, polysiloxane, or polystyrene is proposed in Japanese Patent No. 2,599,497.
On the other hand, a variety of optical parts using resin materials, for example, in production of optical fibers, are produced by spinning. Further, in the case of optical waveguide production, for example, the Japanese Patent No. 2,854,669 discloses a production method by injection molding a core part and casting a clad part and Japanese Patent No. 2,599,497 discloses a production method, which combines photolithography and dry etching.
However, the spinning method can produce only fiber-shapes, and can not produce optical parts with complicated shapes other than fibers, such as a connector, an optical waveguide and the like. Also, although the injection molding and casting can produce optical parts with various shapes it is difficult to produce optical parts having fine and precise patterns using injection molding and casting.
Meanwhile, the method comprising a combination of photolithography with dry etching and/or wet etching, it is possible to produce optical parts having fine and precise patterns. However, this method has the following problems: (1) the production steps are complicated and consequently the productivity is low; (2) wastes (resist, alkaline waste liquid, and the like) generated in a series of the production process are harmful and large in quantity, so that the damage to environments is large and disposal treatment cost of the waste is high; and (3) attributed to the facts (1) and (2), the production cost is high.
On the other hand, the present inventors have proposed image formation methods excellent in resolution and production methods of color filters using electrodeposition materials including coloring materials by electrodeposition by low voltage application or photoelectrodeposition in Japanese Patent Application Laid-Open (JP-A) Nos. 10-119,414, 11-189,899, 11-174,790, 11-133,224, and 11-335,894. These image formation method and color filter formation method can be characterized in that colored films with high resolution can be easily formed, however they are techniques to be applied mainly in the field of display apparatus such as liquid crystal displays.
As compared with the method involving photolithography in combination with dry etching or wet etching, the above-mentioned electrodeposition methods are capable of easily forming fine patterns at high productivity while only generating harmful waste solution in slight amounts. However, producing optical parts of an optical waveguide or the like by an electrodeposition method has not been tried yet.
Further, an electrodepositive polymer material to be employed for a conventional electrodeposition method contains many hydrogen atoms, and thus is insufficient in the light transmissivity in a wavelength region of 700 nm to 1.35 μm, which is expected to become necessary in communication in wavelength range to be used for optical communication, especially in short distance communication in local areas.